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Theme III - 3.2

Advanced large capacity thermal energy storage

Project Leader

M.Lightstone

Description

Effective storage devices must minimize energy losses, facilitate charging and discharging and ensure optimum operation of the associated energy collection and distribution systems. These devices must also be cost effective and of practical design for implementation into new and existing buildings or communities. There are numerous approaches available for thermal energy storage depending on the application, temperature range of energy supply and that required for distribution, and the thermal storage time frame. Storage of energy through sensible storage using water tanks remains a cost effective method of short term or diurnal storage. Large water tanks provide an economic advantage (on a per unit volume measure) as compared to small tanks (Hadorn, 2008b) but the largest tanks (volume of order 30,000 m3) are unable to meet district-heating needs in cold climates. As such, large water tanks have been effectively used in conjunction with borehole fields for longer-term energy storage as shown at the Drake Landing Solar Community (Rysanek & Harrison, 2008) and numerous projects in Germany (Schmidt & Mangold, 2008). Careful design of the large tank geometry, interior baffles, locations of inlet and outlet ports is required to enhance stratification.

Energy storage capacity to volume ratio in thermal storage devices can also be greatly enhanced through the use of phase-change materials (PCM) or thermo-chemical batteries. Numerous challenges exist in the effective integration of PCM or thermo-chemical storage into thermal storage systems. For example, the theoretical advantage of PCMs is often not obtained as a result of the poor sensible energy storage capacity and thermal conductivity of those materials in comparison to that for water. Indeed, Talmatsky and Kribus (2008) concluded from their system simulations that future research in this area must focus on innovative design for the gain in PCMs to be realized. Project 3.2 is concerned with research into the design of large water tanks (including buried water tanks interacting with borehole fields) and the development of improved designs for more compact energy storage.